Spangle.Net.Transport.SRT

An SRT (Secure Reliable Transport) listener and duplex-pipe transport for .NET, built on System.IO.Pipelines. Part of the Spangle streaming media server family.

The NuGet package is fully self-contained: the native libsrt (statically linked with mbedTLS) ships inside for win-x64, win-arm64, linux-x64, linux-arm64 and osx-arm64. No system packages, no vcpkg, nothing to install.

Features

• Truly asynchronous accept — a dedicated thread drives srt_epoll and feeds a bounded channel; await AcceptSRTClientAsync() never blocks a thread pool thread
• Backpressure-aware receive — when the consumer falls behind, the socket is masked out of the epoll set until the pipe drains; memory stays bounded per connection while libsrt buffers within its own receive window
• Zero staging copies — srt_recvmsg writes directly into the pipe's buffer
• IDuplexPipe surface — consume SRT streams with the same PipeReader code you would use for any other transport
• Stream ids — the sender's streamid (the SRT counterpart of an RTMP stream key) surfaces as SRTClient.StreamId, ready for routing and publish authorization
• Encryption — set SRTListenerOptions.Passphrase and only senders presenting the same passphrase can connect; payloads are AES-encrypted on the wire (mbedTLS backend, PBKDF2 key derivation)

Getting Started

dotnet add package Spangle.Net.Transport.SRT

using System.Net;
using Spangle.Net.Transport.SRT;

var listener = new SRTListener(IPEndPoint.Parse("0.0.0.0:9998"), new SRTListenerOptions
{
    Passphrase = "correct horse battery staple", // optional; 10-79 bytes
});
listener.Start();

while (true)
{
    SRTClient client = await listener.AcceptSRTClientAsync(ct);
    // e.g. "srt://host:9998?streamid=live/abc" => route to stream "live/abc"
    Console.WriteLine($"accepted: {client.StreamId}");
    _ = ConsumeAsync(client, ct);
}

static async Task ConsumeAsync(SRTClient client, CancellationToken ct)
{
    using (client)
    {
        while (true)
        {
            var result = await client.Pipe.Input.ReadAsync(ct);
            // e.g. feed result.Buffer (MPEG-TS packets) to a demuxer
            client.Pipe.Input.AdvanceTo(result.Buffer.End);
            if (result.IsCompleted) break;
        }
    }
}

Push a test stream with an SRT-capable ffmpeg:

ffmpeg -re -f lavfi -i testsrc2 -c:v libx264 -f mpegts srt://127.0.0.1:9998

Status

Pre-1.0: the API surface is small and still evolving. Listener/receive comes first; client-side connect is not exposed yet (open an issue if you need it - it will be prioritized immediately).

Native pieces

Component	Version	License
libsrt	pinned tag (see release notes)	MPL-2.0
Mbed TLS	3.6 LTS	Apache-2.0

Both are statically linked, unmodified, into a single srt_interop library per RID and rebuilt from source by CI on native runners for every target. See THIRD-PARTY-NOTICES.txt for the details required by their licenses.

License

This library is under the MIT License. See LICENSE. The bundled native components remain under their own licenses as described above.